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A-Level Physics > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

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1
Q

What is the de Broglie wavelength of an electron?

A

λ ≈ (hc)/E

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2
Q

What must the wavelength be to investigate nuclear radius?

A

Tiny (~10^-15m)

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3
Q

Where does the first minimum appear when investigating nuclear radius?

A

sinθ =1.22λ/2R

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4
Q

What is the plum pudding model of the atom?

A

Atoms were spheres of positive charge with tiny negative chargers inside them

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5
Q

Describe Rutherford’s alpha scattering experiment

A

A circular detector screen set up in front of an alpha source with a strip of gold foil in between

They expected the particles to be deflected by a small amount

Instead most went straight through and some deflected at a large angle

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6
Q

Why in rutherfords experiment did the particles behave the way they did?

A

Alpha particles went straight through because most of an atom is empty space

Some “hit” the nucleus and deflected backwards or sideways due to positivity charges repelling

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7
Q

In rutherfords experiment when is electric potential energy and kinetic energy the same?
What’s the equation to find it

A

Alpha particle is deflected through 180 degrees and will reverse in direction

E = (QGold Qalpha) / 4pie Epsilon nought r

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8
Q

As nucleon number increase what happens to radius?

A

Increases with exponential decay

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9
Q

What’s the equation for nuclear radius being proportional to the cube root of nucleon number

A

R = R• A^(1/3)

Where R• = 1.4

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10
Q

What are the 4 types of nuclear radiation and what do the consist of?

A

Alpha - a helium nucleus
Beta minus - election
Beta plus - positron
Gamma - short wave length, high frequency electromagnetic wave

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11
Q

The density of nuclear matter is enormous

True of false

A

True

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12
Q

What is the ionising strength and speed of the 4 types of nuclear radiation?

A

Alpha - strong and slow
Beta minus - weak and fast
Beta plus - virtually zero
Gamma - very weak and speed of light

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13
Q

Which type of nuclear radiation is not affected by magnetic field?

A

Gamma

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14
Q

What are the types of radiation stopped by?

A

Alpha - paper or few cm of air
Beta minus - 3mm o aluminium
Gamma - many cm of lead or several m of concrete

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15
Q

What is different about beta plus decay compared to the other nuclear radiation?

A

Annihilated by and election which means it has virtually zero range

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16
Q

What is ionisation?

A

Addition or removal of an electron from an atom

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17
Q

What the the ionising properties of alpha particles?

A

Easily pull electrons off atoms

Transfer of energy from the alpha particle to the atom

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18
Q

What the the ionising properties of beta particles?

A

Knocks electrons off atoms due to very high speeds

Used for controlling thickness of materials

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19
Q

What the the ionising properties of gamma rays?

A

Radioactive tracers used to help diagnose patients with the need for surgery
Treatment of cancer Tumours

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20
Q

What damage do the types of nuclear radiation have on the body?

A 
Alpha - will not penetrate skin 
              Very dangerous if 
               Ingested 
Beta - less damage to the body tissue 
Gamma - no effect unless long term exposure
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21
Q

What does a Geiger counter detect?

A

Radiation

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22
Q

What is background radiation?

A

Radiation that is all around us

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23
Q

What are 5 sources of background radiation?

A 
The air 
The ground and buildings 
Cosmic radiation 
Living things 
Man-made radiation
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24
Q

Why is there background radiation in the air?

A

Radon gas released from rocks(alpha)

Usually Largest contributor

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25
Q

All rock contains radioactive isotopes. True or false

A

True

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26
Q

What is cosmic radiation?

A

Cosmic ray particles (Mostly high energy photons) collide with atmosphere

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27
Q

The intensity of gamma radiation obeys what law?

A

Inverse square law

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28
Q

What does the inverse square law mean?

A

Radiation spreads out as you get further away

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29
Q

You should keep the radioactive source as far away from your body as possible? Why is this?

A

Inverse square law

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30
Q

Explain in short 4 points an investigation to show the inverse square law

A
  1. Set up a Geiger counter in front of a meter rule
  2. Place radioactive source (using tongs) at a set distance away and take a reading
  3. Repeat 3 times for an average
  4. Repeat for different distances

Make sure you minus the background radiation!!!!!!!!!

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31
Q

every isotope decays at a different rate

A

i didn’t know how to make this a flash card but it seemed important

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32
Q

radioactive decay is of what distribution?

A

random

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33
Q

can you predict the decay of a single nucleus?

A

no

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34
Q

what is the activity of a sample?

A

the number of nuclei (N) that decay each second

its proportional to the size of the sample

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35
Q

what is activity measured in?

A

becquerels, Bq

1 Bq = 1 decay per second

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36
Q

what is the decay constant symbol?

A

lambda

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37
Q

the bigger the decay constant the …

A

faster the rate of decay

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38
Q

what is the definition of half life?

A

the average time is takes for the number of unstable nuclei to halve

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39
Q

how does the number of undecayed particles decrease?

A

exponentially

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40
Q

how do you find the number of atoms if you are given the molar mass?

A

number of moles multiplied by Avogadro’s constant

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41
Q

what are the 2 main uses of radioactive substances?

A

radioactive dating (carbon 14 has a half-life of 5730 years and starts to decay once a plant dies. it is take in bt living things during photosynthesis) and medical diagnostic (tracers)

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42
Q

when does alpha emission occur?

A

in heavy nuclei e.g. uranium an radium

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43
Q

when does beta minus emission occur?

A

neutron rich nuclei

44
Q

when does gamma radiation occur?

A

too much energy

45
Q

what is emitted in beta minus decay?

A

electron and an antineutrino

46
Q

what happens in beta minus decay

A

neutron changes into a proton

47
Q

What happens in nuclear fission?

A

An unstable nuclei splits into two smaller nuclei, and releases some NEUTRONS and ENERGY

48
Q

what classifies as a large nuclei?

A

at least 83 protons

49
Q

large nuclei split into 2 smaller nuclei what is this?

A

fission

50
Q

why are the 2 types of fission?

A

induced and spontaneous

51
Q

How can we induce fission?

A

By making a neutron enter a Uranium-235 nucleus, causing it to become very unstable

52
Q

What kind of neutrons can be captured for induced fission?

A

Low-energy (“thermal”) neutrons

53
Q

Why is energy released during nuclear fission?

A

Because the new, smaller nuclei have a higher binding energy per nucleon

54
Q

What kind of nuclei are most likely to spontaneously fission?

A

Large ones

55
Q

What limits the number of nucleons that a nucleus can contain?

A

Spontaneous fission

56
Q

What do nuclear reactors use as fuel for fission reactions?

A

Rods of uranium (that are rich in U-235)

57
Q

What isotopes of uranium are found in the uranium rods used for fission reactions?

A

U-235

U-238

58
Q

How are uranium rods placed into the nuclear reactor, and why?

A

Remotely, to keep workers as far away from radiation as possible

59
Q

Describe the chain reaction in nuclear reactors

A

A fission reaction produces more neutrons, which then induce other nuclei to fission, which produces more neutrons, etc.

60
Q

How are produced neutrons slowed down for capture by the uranium nuclei in a chain reaction in a nuclear reactor?

A

By a moderator (e.g. water)

61
Q

What are slowed-down neutrons called?

A

Thermal neutrons

62
Q

What does the moderator do?

A

Slows down neutrons so they can captured by uranium nuclei

63
Q

How does the moderator slow down neutrons?

A

Elastic collisions between the neutrons and nuclei of the moderator material

64
Q

What defines the most efficient materials for being a moderator?

A

Similar mass to the neutrons (e.g. water)

65
Q

What is the minimum amount of fuel you need to make the chain reaction continue on its own at a steady rate?

A

Critical mass

66
Q

What is called when you DON’T have the minimum amount of fuel you need to make the chain reaction continue on its own at a steady rate?

A

Sub-critical mass

67
Q

What is the amount of fuel a nuclear reactor uses called?

A

Supercritical mass

68
Q

How do you control the rate of fission in a nuclear reactor?

A

Inserting control rods at varying rates

69
Q

How do control rods control the chain reaction?

A

Limiting the number of neutrons in the reactor

They absorb neutrons so that the rate of fission is controlled

70
Q

What are control rods made of?

A

A material that absorbs neutrons (e.g. boron)

71
Q

How do you shut down a nuclear reactor in an emergency?

A

Releasing all of the control rods into the reactor

72
Q

How is produced heat removed form the nuclear reactor?

A

Using a coolant

often the same water used as the moderator

73
Q

How can a nuclear reactor be used to generate electricity?

A

Heat from the reactor is used by the coolant to make steam for powering electricity-generating turbines

74
Q

How do you prevent radiation from escaping the nuclear reactor?

A

Shielding, often a concrete case

75
Q

How do you reduce the risks involved with using nuclear power?

A

Shielding and control rods

76
Q

How can explosions happen in a nuclear reactor?

A

Runaway chain reaction

77
Q

Why is nuclear fission better than fossil fuels?

A

Creates less greenhouse gases

78
Q

Why is nuclear fission worse than fossil fuels?

A

Lots of dangerous waster products

79
Q

What do the waster products of nuclear fission contain?

A

High-neutron isotopes, making them unstable and radioactive

80
Q

How can the waste products of nuclear fission be useful?

A

Tracers in medical diagnosis

81
Q

What is the temperature of material removed from a reactor?

A

Very hot

82
Q

How is material removed from the reactor cooled?

A

Remotely placed into a cooling pond

83
Q

How is radioactive waste stored?

A

In sealed containers until activity has reduced

84
Q

What is nuclear fusion?

A

Two light nuclei combine to create a larger nucleus

85
Q

Why is energy released during nuclear fusion?

A

The new nuclei has a much higher binding energy per nucleon

86
Q

What is the charge on all nuclei?

A

Positive

87
Q

Why do nuclei need lots of energy to fuse?

A

There is an electrostatic force of repulsion between all nuclei that must be overcome
to get close enough to fuse

88
Q

What fundamental interaction occurs during nuclear fusion?

A

Strong interaction holds the nuclei together

89
Q

How much kinetic energy is needed to make two nuclei fuse together?

A

About 1 MeV

90
Q

What happens to low-energy nuclei, that try to get close enough for nuclear fusion?

A

Deflected by electrostatic repulsion

91
Q

What happens to high-energy nuclei, that try to get close enough for nuclear fusion?

A

Overcome electrostatic repulsion and are attracted by the strong interaction

92
Q

What is the mass defect?

A

Mass of nucleus is less than the mass of its constituent parts
(The difference is the mass defect)

93
Q

What happens to the the lost mass of a nucleus when nucleons join together?

A

Converted into energy and relased

94
Q

What is the energy released when nucleons join together equivalent to?

A

Mass defect

95
Q

How much energy is required to pull a nucleus completely apart?

A

The same as the energy released when the nucleus is formed

96
Q

What is the binding energy divided by the mass defect equal to?

A

About 931.5 MeVu⁻¹

97
Q

At what value of N is Average Binding Energy Per Nucleon at a maximum?

A

N = 56

Iron

98
Q

What is the average binding energy per nucleon equal to?

A

Binding energy divided by nucleon number

99
Q

What element is the most stable nuclei?

A

Iron

100
Q

What happens to the left of Iron on the Binding Energy-Nucleon Number graph?

A

Fusion

101
Q

What happens to the right of Iron on the Binding Energy-Nucleon Number graph?

A

Fission

102
Q

What does the change in Average Binding Energy give?

A

Energy Released

103
Q

What is energy released equal to?

A

Average binding energy

104
Q

Why is ionising radiation dangerous?

A

It ionises body tissue, causing damage

105
Q

Why are alpha-sources suitable for smoke alarms?

A

They allow current to flow, but won’t travel very far.

106
Q

What kind of source is best for smoke alarms?

A

Alpha-sources

107
Q

Why might a nucleus be unstable?

A

Too many neutrons
Too few neutrons
Too many nucleons
Too much energy

A-Level Physics (13 decks)

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